1. Field of the Invention
The present invention relates to a novel discharge lamp which comprises an arc tube for high pressure discharge and a discharge gap for discharging until restarting the arc tube and the discharge gap being electrically connected in parallel to the arc tube in an outer bulb and a novel lighting equipment for operating the discharge lamp on a high frequency operating device.
2. Description of the Prior Arts
Recently, various lighting equipments for saving energy have been studied in view of energy saving.
Among various light sources, incandescent lamps have been mainly used, however overall efficacy is lowest. The requirement for saving energy as light sources is remarkably high. It has been desired to develop a light source having higher efficacy whereby the incandescent lamps can be replaced. The high pressure discharge lamps such as a high pressure mercury vapor discharge lamp, a metal halide vapor discharge lamp and a high pressure sodium vapor discharge lamp have each efficacy of 3 to 10 times of the efficacy of the incandescent lamp and have each configuration similar to that of the incandescent lamp. Therefore, it seems to be suitable to replace the incandescent lamps with the high pressure discharge lamps. In the case of high pressure discharge lamp, however, the pressure of mercury vapor in the arc tube during the steady operation of the lamp, reaches several atmospheres. When the lamp is extinguished by a transient voltage drop or a transient interruption of the power supply the lamp can not immediately initiate a discharge even though the power supply is recovered to the normal state. The lamp could not initiate a discharge again until the pressure of mercury vapor in the discharge lamp is lowered adequately in accordance with the decrease of arc tube temperature. The time from the extinction of the lamp to the restarting is referred to as a restarting time. The restarting time is required for 3 to 5 minutes in the case of the high pressure mercury vapor discharge lamp; for 8 to 15 minutes in the case of the metal halide vapor discharge lamp; and for 2 to 15 minutes in the case of the high pressure sodium vapor lamp. Such long restarting time causes trouble in replacing the incandescent lamp with said discharge lamps. When the high pressure discharge lamp is operated, a ballast is required. The ballast is in a large size and is placed out of the discharge lamp. It has been difficult to replace the incandescent lamp with a combination of the ballast and the discharge lamp in the practical application.